Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks

From: Pavel Machek <pavel@ucw.cz>
To: Miroslav Benes <mbenes@suse.cz>
Cc: jpoimboe@redhat.com, jeyu@kernel.org, jikos@kernel.org,
	pmladek@suse.com, lpechacek@suse.cz,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
	Oleg Nesterov <oleg@redhat.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks
Date: Mon, 6 Nov 2017 12:08:33 +0100	[thread overview]
Message-ID: <20171106110833.GB24863@amd> (raw)
In-Reply-To: <20171031114853.841-2-mbenes@suse.cz>

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Hi!

> --- a/Documentation/ABI/testing/sysfs-kernel-livepatch
> +++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
> @@ -33,6 +33,15 @@ Contact:	live-patching@vger.kernel.org
>  		An attribute which indicates whether the patch is currently in
>  		transition.
>  
> +What:		/sys/kernel/livepatch/<patch>/signal
> +Date:		Oct 2017
> +KernelVersion:	4.15.0
> +Contact:	live-patching@vger.kernel.org
> +Description:
> +		A writable attribute that allows administrator to affect the
> +		course of an existing transition. Writing 1 sends a signal to
> +		all remaining blocking tasks.

What kind of signal?

>  What:		/sys/kernel/livepatch/<patch>/<object>
>  Date:		Nov 2014
>  KernelVersion:	3.19.0
> diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
> index ecdb18104ab0..6694530d0894 100644
> --- a/Documentation/livepatch/livepatch.txt
> +++ b/Documentation/livepatch/livepatch.txt
> @@ -178,6 +178,12 @@ transition, it shows -1.  Any tasks which are blocking the transition
>  can be signaled with SIGSTOP and SIGCONT to force them to change their
>  patched state.
>  
> +Administrator can also affect a transition through
> +/sys/kernel/livepatch/<patch>/signal attribute. Writing 1 to the attribute sends
> +a signal to all remaining blocking tasks. This is an alternative for
> +SIGSTOP/SIGCONT approach mentioned in the previous paragraph. It should also be
> +less harmful to the system.

Well... If SIGSTOP / SIGCONT is considered harmful (it probably is),
it should be mentioned above, and not in note here...
									Pavel

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